The invention relates to a method for treating in particular viscous-pasty compositions in a housing with kneading elements, at least one kneading element being monitored.
Such devices are also referred to as mixing kneaders. They serve for a wide variety of different purposes. To be mentioned first is evaporation with solvent recovery, which is performed batchwise or continuously and often also under a vacuum. This is used for example for treating distillation residues and in particular toluene diisocyanates, but also production residues with toxic or high-boiling solvents from the chemical industry and pharmaceutical production, wash solutions and paint slurries, polymer solutions, elastomer solutions from solvent polymerization, adhesives and sealing compositions.
The apparatuses are also used for carrying out continuous or batchwise contact drying of products that are moist with water and/or solvents, often likewise under a vacuum. Intended applications are especially for pigments, dyes, fine chemicals, additives, such as salts, oxides, hydroxides, antioxidants, temperature-sensitive pharmaceutical and vitamin products, active substances, polymers, synthetic rubbers, polymer suspensions, latex, hydrogels, waxes, pesticides and residues from chemical or pharmaceutical production, such as salts, catalysts, slags and waste liquors. Other applications for these methods are in food production, for example the production and/or treatment of block milk, sugar substitutes, starch derivatives, alginates, for the treatment of industrial slurries, oil slurries, bio slurries, paper slurries, paint slurries and generally for the treatment of tacky, crust-forming viscous-pasty products, waste products and cellulose derivatives.
In mixing kneaders, degassing and/or devolatilization can take place. This is applied to polymer melts, after condensation of polyester or polyamide melts, to spinning solutions for synthetic fibers and to polymer or elastomer granules or powder in the solid state.
In a mixing kneader, a polycondensation reaction can take place, usually continuously and usually in the melt, and is used especially in the treatment of polyamides, polyesters, polyacetates, polyimides, thermoplastics, elastomers, silicones, urea resins, phenolic resins, detergents and fertilizers.
A polymerization reaction can also take place, likewise usually continuously. This is applied to polyacrylates, hydrogels, polyols, thermoplastic polymers, elastomers, syndiotactic polystyrene and polyacrylamides.
Quite generally, solid, liquid and multi-phase reactions can take place in the mixing kneader. This applies especially to back-reactions, in the treatment of hydrofluoric acid, stearates, cyanates, polyphosphates, cyanuric acids, cellulose derivatives, cellulose esters, cellulose ethers, polyacetal resins, sulfanilic acids, Cu-phthalocyanines, starch derivatives, ammonium polyphosphates, sulfonates, pesticides and fertilizers.
Furthermore, solid/gas reactions (for example carboxylation) or liquid/gas reactions can take place. This is applied in the treatment of acetates, azides, Kolbe-Schmitt reactions, for example BON, Na-salicylates, parahydroxybenzoates and pharmaceutical products.
Liquid/liquid reactions take place in the case of neutralization reactions and transesterification reactions.
Dissolution and/or degassing takes place in such mixing kneaders in the case of spinning solutions for synthetic fibers, polyamides, polyesters and celluloses.
What is known as flushing takes place in the treatment or production of pigments.
A solid-state post-condensation takes place in the production or treatment of polyesters and polyamides, a continuous slurrying for example in the treatment of fibers, for example cellulose fibers, with solvents, a crystallization from the melt or from solutions in the treatment of salts, fine chemicals, polyols, alcoholates, a compounding or mixing (continuously and/or batchwise) in the case of polymer mixtures, silicone compositions, sealing compositions or fly ash, and a coagulation (in particular continuously) in the treatment of polymer suspensions.
In a mixing kneader, multi-functional processes can also be combined, for example heating, drying, melting, crystallizing, mixing, degassing, reacting—all of these continuously or batchwise. Substances which are produced or treated by this means are polymers, elastomers, inorganic products, residues, pharmaceutical products, food products and printing inks.
In mixing kneaders, vacuum sublimation/desublimation can also take place, whereby chemical precursors, for example anthraquinone, metal chlorides, organometallic compounds etc. are purified. Furthermore, pharmaceutical intermediates can be produced.
A continuous carrier-gas desublimation takes place, for example, in the case of organic intermediates, for example anthraquinone and fine chemicals.
A distinction is substantially made between single-shaft and dual-shaft mixing kneaders. A single-shaft mixing kneader is described for example in EP 91 405 497.1. Multi-shaft mixing and kneading machines are described in CH-A 506 322, EP 0 517 068 B, DE 199 40 521 A1 or DE 101 60 535. In this machine, radial disk elements and axially oriented kneading bars arranged between the disks are located on a shaft. Mixing and kneading elements shaped in a frame-like manner engage between said disks from the other shaft. These mixing and kneading elements clean the disks and kneading bars of the first shaft. The kneading bars on both shafts in turn clean the inner wall of the housing.
U.S. Pat. No. 4,504,150 A discloses an extruder for kneading and extruding a synthetic material, a corresponding extruder screw being arranged rotatably in a cylindrical housing. Inserted between the screw flights are pins, with which the mass flow is to be monitored. In this case, a deformation of these pins is determined. Something similar is shown in DE 35 02 437 A1.
U.S. Pat. No. 4,508,454 A likewise shows an extruder, corresponding pins extending into recesses that are formed in the helix of the extruder screw. It is intended here to determine breakage of the pins, which may take place for example due to metal particles in the extrudate.
A mixing kneader of the type according to the invention is shown in DE 43 03 852 A1. In this document, the monitoring of kneading elements for breakage or similar damage is described. This may concern for example a small tube that is arranged in the kneading element and is pressurized or evacuated. In this case, this pressure or the vacuum is monitored.
The problem addressed by the present invention is that of making the operation of such a device according to the invention more reliable and trouble-free.